a) Field of the Invention
The present invention relates to a diclofenac sodium plaster containing diclofenac sodium and having good percutaneous absorption.
b) Description of the Related Art
Diclofenac sodium is a non-steroidal anti-inflammatory analgesic and is now available as oral preparations and suppositories on the market. However, oral or rectal administration involves the problem of various side effects, led by stomach troubles, while suppositories are accompanied by the problem of shock or the like which may be caused by an abrupt increase in the diclofenac concentration in blood. To overcome such problems, formulations for external use, such as ointments, creams and liquid preparations, have been proposed with a view to allowing diclofenac sodium to act locally or on the whole body. In practice, however, there is no external preparation with good percutaneous absorption.
The present inventors previously found that a gel-type ointment having excellent percutaneous absorption can be obtained by adding diclofenac or a salt thereof (and menthol) to a gel-form base which has been obtained by neutralizing a gelling agent with ammonia or an alkylamine, and filed a patent application there-on (Japanese Patent Application Laid-Open No. 49722/1990.
The gel-type ointment is however accompanied by the drawback that, even when a gel-type ointment excellent in percutaneous absorption as described above is used, its stable percutaneous absorption over a long period of time is difficult because the gel-type ointment is prone to separation, for example, due to contact between the skin of an applied part and clothing, washing, or the like. In addition, it is difficult to spread such an ointment in a predetermined constant amount and at a constant thickness on the skin, leading to the further drawback that it is difficult to maintain stable percutaneous absorption over a long time.
The present inventors therefore have proceeded with a further investigation. As a result, the use of a plaster has been found most suitable as a method for extended stable percutaneous absorption of diclofenac.
A paste for plasters, however, is required to have many functions and properties beyond that of carrying an effective ingredient. It is therefore impossible to divert, for example, gel-type ointments which have been employed conventionally. Functions and properties required for a paste for plasters include having suitable adhesiveness when applied to the skin, locational stability during long-term application, easy release from the skin when the plaster is removed, and stability of properties even when stored as a product for a long time. Numerous limitations are therefore imposed on the composition of a paste.